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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Local spring effect in titanium-based layered oxides

Titanium-based layered oxides (TLOs) are one of the most promising electrode material families for sodium-ion batteries (NIBs) due to their smooth charge/discharge profiles and excellent cycle performance. However, the reaction mechanism of these materials, especially the reason for the disappearance of multiple voltage plateaus, is still not clear. Herein, two representative TLOs (Na 2/3 Ni 1/3 Ti 2/3 O 2 and Na 2/3 Co 1/3 Ti 2/3 O 2 ) with the same P2 crystal structure have been studied to scrutinize those unexplained issues. In situ synchrotron high-energy X-ray diffraction revealed a solid solution reaction mechanism for both, suggesting the absence of rigid phase transitions upon electrochemical cycling. An interesting “spring effect” of the TiO 6 octahedron, i.e., the reversible vibration of the central Ti atom inside the local octahedron upon electrochemical redox, was demonstrated by advanced X-ray absorption spectroscopy and theoretical calculations. Such an effect could suppress the rigid phase transitions, and result in smooth charge/discharge profiles and enhanced cycle stability. Finally, this work not only accounts for the disappearance of multiple voltage plateaus of TLOs for NIBs, but also provides an effective local-structure viewpoint to increase the cycle stability of electrode materials for other advanced battery systems.

25 ENERGY STORAGE↗
DOE OSTI2021

Trimeron-phonon coupling in magnetite

Using density functional theory, we study the lattice dynamical properties of magnetite (Fe 3 O 4 ) in the high-temperature cubic and low-temperature monoclinic phases. The calculated phonon dispersion curves and density of states are compared with the available experimental data obtained by inelastic neutron, inelastic x-ray, and nuclear inelastic scattering. We find a very good agreement between the theoretical and experimental results for the monoclinic Cc structure revealing the strong coupling between the charge-orbital (trimeron) order and specific phonon modes. For the cubic phase, clear discrepancies arise due to fluctuation effects, which are not included in the calculation method. Despite this shortcoming, we argue that the main spectral features can be understood assuming that the strong trimeron-phonon coupling is extended above the Verwey transition, with lattice dynamics influenced by the short-range order instead of the average cubic structure. Our results indicate the validity of trimerons (and trimeron-phonon coupling) to explain the physics of magnetite much beyond their original formulation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dynamic x-ray diffraction and nanosecond quantification of kinetics of formation of β -zirconium under shock compression

We report the atomic- and nanosecond-scale quantification of kinetics of a shock-driven phase transition in Zr metal. We uniquely make use of a multiple shock-and-release loading pathway to shock Zr into the β phase and to create a quasisteady pressure and temperature state shortly after. Coupling shock loading with in situ time-resolved synchrotron x-ray diffraction, we probe the structural transformation of Zr in the steady state. Our results provide a quantified expression of kinetics of formation of β-Zr phase under shock loading: transition incubation time, completion time, and crystallization rate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1978

Field ionization kinetic and electron impact studies of gas phase transition states - The cyclic bromonium ion

Cis- and trans-isomers of 4-t-butylcyclohexyl bromide were studied to determine the mechanism of cyclic bromonium ion formation. The field ionization kinetic and electron impact data indicate that the formation of the cyclic structure occurs simultaneously with loss of the neutral fragment. The data also show that little or no gas-phase cis-trans isomerization occurs.

Green, M. M.↗
DOE OSTI2020

Ultrafast dynamics in the high-symmetry and in the charge density wave phase of 2 H –NbSe 2

Here we investigate carrier and collective mode dynamics in 2H-NbSe 2 using time-resolved optical pump-probe spectroscopy and compare the results with first-principles calculations. Broadband ultrafast reflectivity studies of 2H-NbSe 2 in a wide temperature interval covering the normal, charge density wave (CDW) and superconducting phase were performed. Spectral features observed in the transient reflectivity experiment were associated with specific optical transitions obtained from band structure calculations. Displacive excitation of coherent phonons showed CDW-associated coherent oscillations of the soft phonon mode across the whole spectral range. Temperature evolution of this coherent phonon mode in the low-excitation linear regime shows softening of the mode down to the CDW transition temperature T CDW with subsequent hardening below T CDW . The global fit of the broadband probe data reveals four different relaxation times associated with characteristic electron-electron, electron-phonon, and phonon-phonon relaxation processes. From first-principles calculations of electron-phonon coupling we associate the few picosecond electron-phonon relaxation time $\tau_2$ with a specific group of phonons with frequencies around 20 meV. On the other hand, the anomalously long relaxation time of $\tau_3 \sim$ to 100 ps is associated with anharmonicity-driven phonon-phonon scattering. All relaxation processes result from anomalies near the second order CDW phase transition that are reflected in the temperature dependencies of the characteristic relaxation times and amplitudes of coherent oscillations. At the highest fluences we observe electronic melting of the CDW and disappearance of the mode hardening below T CDW .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Atomistic Insights of Irreversible Li + Intercalation in MnO 2 Electrode

Tunnel-structured MnO 2 represents open-framed electrode materials for reversible energy storage. Its wide application is limited by its poor cycling stability, whose structural origin is unclear. We tracked the structure evolution of β-MnO 2 upon Li + ion insertion/extraction by combining advanced in situ diagnostic tools at both electrode level (synchrotron X-ray scattering) and single-particle level (transmission electron microscopy). The instability is found to originate from a partially reversible phase transition between β-MnO 2 and orthorhombic LiMnO 2 upon lithiation, causing cycling capacity decay. Moreover, the MnO 2 /LiMnO 2 interface exhibits multiple arrow-headed disordered regions, which severely chop into the host and undermine its structural integrity. Our findings could account for the cycling instability of tunnel-structured materials, based on which future strategies should focus on tuning the charge transport kinetics toward performance enhancement.

25 ENERGY STORAGE↗
DOE OSTI2021

Sub-10 nm Probing of Ferroelectricity in Heterogeneous Materials by Machine Learning Enabled Contact Kelvin Probe Force Microscopy

Reducing the dimensions of ferroelectric materials down to the nanoscale has strong implications on the ferroelectric polarization pattern and on the ability to switch the polarization. As the size of ferroelectric domains shrinks to the nanometer scale, the heterogeneity of the polarization pattern becomes increasingly pronounced, enabling a large variety of possible polar textures in nanocrystalline and nanocomposite materials. Critical to the understanding of fundamental physics of such materials and hence their applications in electronic nanodevices is the ability to investigate their ferroelectric polarization at the nanoscale in a nondestructive way. We show that contact Kelvin probe force microscopy (cKPFM) combined with a k-means response clustering algorithm enables to measure the ferroelectric response at a mapping resolution of 8 nm. In a BaTiO 3 thin film on silicon composed of tetragonal and hexagonal nanocrystals, we determine a nanoscale lateral distribution of discrete ferroelectric response clusters, fully consistent with the nanostructure determined by transmission electron microscopy. Moreover, we apply this data clustering method to the cKPFM responses measured at different temperatures, which allows us to follow the corresponding change in the polarization pattern as the Curie temperature is approached and across the phase transition. This work opens up perspectives for mapping complex ferroelectric polarization textures such as curled/swirled polar textures that can be stabilized in epitaxial heterostructures and more generally for mapping the polar domain distribution of any spatially highly heterogeneous ferroelectric materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Topological origin of phase separation in hydrated gels

Depending on their composition, hydrated gels can be homogeneous or phase-separated, which, in turn, affects their dynamical and mechanical properties. However, the nature of the structural features, if any, that govern the propensity for a given gel to phase-separate remains largely unknown. Here, we argue that the propensity for hydrated gels to phase-separate is topological in nature. We employ reactive molecular dynamics simulations to model the early-age precipitation of calcium–alumino–silicate–hydrate (Csingle bondAsingle bondSsingle bondH) gels with varying compositions, i.e., (CaO) 1.7 (Al 2 O 3 ) x (SiO 2 ) 1 – x (H 2 O) 3.7 + x . By adopting topological constraint theory, we investigate the structural origin of phase separation in hydrated gels. We report the existence of a homogeneous-to-phase-separated transition, wherein Si-rich (x ≤ 0.10) Csingle bondAsingle bondSsingle bondH gels are homogeneous, whereas Al-rich (x > 0.10) Csingle bondAsingle bondSsingle bondH gels tend to phase-separate. Furthermore, we demonstrate that this transition is correlated to a topological flexible-to-rigid transition within the atomic network. Finally, we reveal that the propensity for topologically-overconstrained gels to phase-separate arises from the existence of some internal stress within their atomic network, which acts as an energy penalty that drives phase separation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Structure and Superconductivity of Hydrogenated TiZr Alloys Under High Pressure

The effects of pressure on the structure and electrical transport properties, including electrical resistance and critical magnetic field values for superconductivity in pristine and hydrogenated TiZr alloys, were investigated. As pressure increased from ambient to 55 GPa, the structure of the pristine TiZr alloys transformed from hcp to bcc via an intermediate ω phase. The superconducting transition temperature (T c ) significantly increased from 1.76 K at ambient pressure to 15.5 K at 52.2 GPa, accompanied by an extrapolated upper critical field of 24.5 T at T = 0 K. In contrast, the hydrogenated samples exhibited substantially lower T c values compared to the pristine ones, with a T c of 4.6 K at 50.5 GPa and an extrapolated upper critical field of 1.8 T at T = 0 K. Upon decompression, the superconductivity in the hydrogenated sample persisted down to 25 GPa, disappearing when the pressure was reduced to 19 GPa. Synchrotron X-ray diffractions (XRD) analysis revealed the formation of three hydrides: I4/mmm-(Ti, Zr)H 2 , P6 3 /mmc-(Ti, Zr)H 3 , and I4̅3d-(Ti,Zr) 4 H 15 . Finally, by combining XRD and electrical resistance data, we tentatively propose that the P6 3 /mmc-(Ti, Zr)H 3 predominantly induces superconductivity. In contrast to superhydrides, where electron–phonon interactions increase the superconducting temperature at high pressure, hydrogen atoms in hcp-(Ti, Zr)H 3 reduce T c .

36 MATERIALS SCIENCE↗
DOE OSTI2026

Anisotropic multi- Q order in Co x TaS 2

The cobalt-intercalated transition metal dichalcogenide Co x TaS 2 hosts a rich landscape of magnetic phases that depend sensitively on x. While the stoichiometric compound with x = 1/3 exhibits a single magnetic transition, samples with x≤0.325 display two transitions with an anomalous Hall effect (AHE) emerging in the lower temperature phase. Here, we resolve the spin structure in each phase by employing a suite of magneto-optical probes that include the discovery of anomalous magneto-birefringence: a spontaneous time-reversal sensitive rotation of the principal optic axes. A symmetry-based analysis identifies the AHE-active phase as an anisotropic (2+1)Q state, in which magnetic modulation at one wavevector (Q) differs in symmetry from that at the remaining two. The (2+1)Q state naturally exhibits scalar spin chirality as a mechanism for the AHE and expands the classification of multi-Q magnetic phases.

Kruppe, Jonathon [University of California, Berkel↗
DOE OSTI2025

Plumbene: a comprehensive review of theoretical and experimental advances

Plumbene, a two-dimensional (2D) material consisting of a single layer of lead (Pb) atoms in a honeycomb lattice, stands as a pioneering addition to the elemental 2D material family. Here, this comprehensive review encapsulates the theoretical predictions and experimental advancements that underscore its potential. With properties shaped by significant spin-orbit coupling and structural buckling, plumbene offers a playground for phenomena like the quantum spin Hall effect, superconductivity, and topological phase transitions. Despite promising theoretical insights, experimental realization has encountered challenges, primarily due to high reactivity of Pb and the need for precise fabrication conditions. This paper critically examines the electronic, thermal, mechanical, and topological attributes of plumbene, alongside synthesis methods, functionalization techniques, and substrate effects. It further proposes directions for addressing synthesis challenges and integrating plumbene into advanced technologies, particularly in electronic, spintronic, and quantum computing applications. This review aims to bridge the gap between theoretical potential and experimental progress, fostering a deeper understanding of this intriguing material.

2D materials↗
DOE OSTI2024

Emergence of two distinct phase transitions in monolayer CoSe2 on graphene

Abstract Dimensional modifications play a crucial role in various applications, especially in the context of device miniaturization, giving rise to novel quantum phenomena. The many-body dynamics induced by dimensional modifications, including electron-electron, electron-phonon, electron-magnon and electron-plasmon coupling, are known to significantly affect the atomic and electronic properties of the materials. By reducing the dimensionality of orthorhombic CoSe 2 and forming heterostructure with bilayer graphene using molecular beam epitaxy, we unveil the emergence of two types of phase transitions through angle-resolved photoemission spectroscopy and scanning tunneling microscopy measurements. We disclose that the 2 × 1 superstructure is associated with charge density wave induced by Fermi surface nesting, characterized by a transition temperature of 340 K. Additionally, another phase transition at temperature of 160 K based on temperature dependent gap evolution are observed with renormalized electronic structure induced by electron-boson coupling. These discoveries of the electronic and atomic modifications, influenced by electron-electron and electron-boson interactions, underscore that many-body physics play significant roles in understanding low-dimensional properties of non-van der Waals Co-chalcogenides and related heterostructures. Graphical Abstract

36 MATERIALS SCIENCE↗
NASA NTRS2008

The Herschel Oxygen Project: Herschel Space Observatory Open Time Key Project

Topics include: Why oxygen and why at submillimeter wavelengths; gas phase chemistry for water, oxygen, and carbon monoxide is relatively simple; molecular oxygen structure; lower rotational levels and transitions of oxygen; oxygen abundance in interstellar clouds; SWAS spectra of terrestrial oxygen; what Herschel offers HOP; key regions for probing oxygen in the dense interstellar medium; HOP sources and strategy; and HOP data and analysis.

astrochemistry↗
DOE OSTI2024

Magnetic structure and properties of the compositionally complex perovskite (Y 0.2 La 0.2 Pr 0.2 Nd 0.2 Tb 0.2 )MnO 3

Large configurational disorder in compositionally complex ceramics can lead to unique functional properties that deviate from traditional rules of alloy mixing. In recent years, compositionally complex oxides (CCOs) have shown intriguing magnetic behavior including long-range order, enhanced magnetic exchange couplings, and mixed phase magnetic structures. This work focuses on how large local spin disorder affects magnetic ordering in a CCO. Specifically, we investigated the A-site alloyed perovskite, (Y 0.2 La 0.2 Pr 0.2 Nd 0.2 Tb 0.2 )MnO 3 , or (5A)MnO 3 , using a combination of bulk magnetometry, synchrotron X-ray diffraction, and temperature-dependent neutron diffraction. The five A-site ions have an average spin and ionic radius nearly equal to that of Nd 3+ ions, which minimizes structural distortions and allows for an understanding of the local spin disorder effects through a direct comparison with NdMnO 3 . Our magnetometry data show that (5A)MnO 3 exhibits two distinct phase transitions associated with the A-site and B-site sublattices, as seen in NdMnO 3 , as well as the presence of domain pinning and exchange bias at low temperature, suggesting a mixed phase magnetic ground state, as seen in other magnetic CCOs. Neutron powder diffraction shows clear long-range antiferromagnetic ordering below 67 K and refines to a Pn'ma' magnetic structure at low temperature, in excellent agreement with the well-studied behavior of NdMnO 3 . The two most notable differences in (5A)MnO 3 magnetism apparent from our data are a slight suppression of the B-site ordering temperature, which is explained by a smaller Mn–O–Mn bond angle in (5A)MnO 3 than NdMnO 3 , and the presence of a magnetic susceptibility transition above the B-site ordering, which could indicate the formation of a cluster glass but requires further study. Finally, this work demonstrates a general method of isolated investigation of size and spin disorder in CCOs and motivates future work using local structure probes to better understand the effects of nanoscale clustering and local spin disorder in magnetic CCOs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Phase transition in two-dimensional monolayer (1L)-molybdenum disulfide induced by atomic S-basal plane gliding via synchrotron X-ray monochromatic beam radiation for superior electronic performance

Here, in this work, we report a novel approach to reduce the channel resistance by inducing a phase transition behavior from 2H to 1T in a monolayer MoS 2 (1L-MoS 2 ) by a synchrotron X-ray monochromatic beam (mono-beam) radiation. The effects of the biphase structure by the mono-beam on the 1L-MoS2 film were investigated using Raman spectra, photoluminescence (PL) spectra, scanning tunneling microscopy, and scanning tunneling spectroscopy, respectively. Through material characterization, we identified that the lateral sliding of S-vacancies along the S-plane in the 1L-MoS 2 is the key reason for the origin of unidirectional phase transition. The precise phase engineering triggered by the mono-beam radiation process allows the realization of field-effect transistors (FET) with 2X improvement in mobility toward a high on/off ratio (~10 8 ) and a near-ideal subthreshold swing of ~88 mV per decade. The validity of the phase engineering could be further extended for its application as a memory device, exhibiting a gate tunable conduction modulation behavior and a high resistance ratio of ~10 2 at a gate bias of 5 V with endurance of ~100 cycles. Furthermore, an artificial neural network using the synaptic weight update with accuracy of ~93 % was achieved.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Kinetic analyses for solid-state phase transition of metastable amorphous-AlO x (2.5 < x ≤ 3.0) nanostructures into crystalline alumina polymorphs

Solid-solid phase change materials (SS-PCMs) hold promise for energy storage/dissipation in batteries and energetic materials. Yet, phase change kinetics for SS-PCMs undergoing metastable to semi-stable/stable phase transformations remain relatively ill-studied because trapping metastable phases remain challenging. Recently, we demonstrated the kinetic entrapment and stabilization of a highly disordered and amorphous Al-oxide phase m-AlO x @C (x~2.5-3.0) via laser ablation synthesis in solution (LASiS). We report here, to our knowledge, the first chemical kinetics analysis for S-S phase transition of the m-AlO 3 @C nanocomposites (< 5–8 nm sizes) into semi-stable equilibrium alumina phases (θ/γ-Al 2 O 3 ) via disproportionation reaction, while releasing excess trapped gases. Our results indicate the atomic density of the AlO 3 structures to be ~5–10 times less than that of the final Al 2 O 3 phases, which led to the hypothesis of a volume shrinkage process during their phase transition. Temperature-dependent X-ray diffraction studies reveal the high-temperature phase transition for m-AlO 3 → θ/γ-Al 2 O 3 to follow contracting volume kinetics model, thereby validating our earlier hypothesis. Using the geometric volume contraction model, reaction kinetics analyses from Arrhenius plots reveal the activation energy barrier for the phase transition to be ~270±11 kJ/mol. This makes the activation energy barrier nearly identical to the oxidation of micron-sized Al particles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Pressure-dependent phase transitions in hybrid improper ferroelectric Ruddlesden-Popper oxides

The temperature-dependent phase transitions in Ruddlesden-Popper oxides with perovskite bilayers have been under increased scrutiny in recent years due to the so-called hybrid improper ferroelectricity that some chemical compositions exhibit. However, little is currently understood about the hydrostatic pressure dependence of these phase transitions. Herein we present the results of a combined high-pressure powder synchrotron x-ray diffraction experiment and a b i n i t i o study on the bilayered Ruddlesden-Popper phases Ca 3 Mn 2 O 7 and Ca 3 Ti 2 O 7 . In both compounds we observe a first-order phase transition, that in combination with our density functional theory calculations, we can confidently assign as being between polar A 2 1 a m and nonpolar A c a a structures. Interestingly, we show that while the application of pressure ultimately favors a nonpolar phase, as is commonly observed for proper ferroelectrics, regions of response exist where pressure actually acts to increase the polar mode amplitudes. The reason for this can be untangled by considering the varied response of octahedral tilts and rotations to hydrostatic pressure and their trilinear coupling with the polar instability. Published by the American Physical Society 2024

Materials Science↗